A user interface for a portable electronic device includes an input device, such as a keypad, for data input by a user and a flat-panel display for information output to the user. A portable electronic device has an increasing number of features and, as a result, requires more frequent interaction and use of its keypad and display. These features include Internet access, personal organizer functions, entertainment programs, audio player functions (such as MP3 and AM/FM radio), A/V player functions (such as video streaming and video conferencing), calculator functions and a host of other possibilities. As such, the backlighting system for the display and the keypad is activated and remains on for as long as the keypad receives input from the user. When keypad activity is not detected for a particular period of time, such as 15 seconds or so, the backlighting system for display and keypad will deactivate. However, the user has no real need for activating the backlighting system when the ambient lighting conditions are sufficient to view the display and keypad. Thus, in an environment that has sufficient ambient lighting, backlighting becomes a wasteful drain on the battery of the device.
Devices having circuitry for adjusting the luminance of a display based on ambient lighting conditions are known. Such device includes a liquid crystal display, a backlighting source adjacent to the display, and an ambient light sensor coupled to the backlighting source. The backlighting source adjusts the luminance of the liquid crystal display based on the ambient lighting conditions detected by the ambient light sensor. These devices are more energy efficient than systems that turn-on the backlighting source and stay-on for a predetermined time period whenever keypad activity is detected.
Typically, a user has difficulty viewing the display and keypad of the portable electronic device in areas of low lighting or total darkness. In such case, a keystroke is necessary to activate the backlighting system so that the user will be able to read the display and keypad. Unfortunately, the keystroke activates an operation of the device as well as activating the backlighting system. In many cases, the device executes an undesirable operation (such as entering a character on the display), particular since the user could not see the keypad when the keystroke was made. Subsequently, the user must clear the undesired entry in order to continue, thus causing counter-productive keystrokes and wasteful drain on the battery due to these extra keystrokes.
Accordingly, there is a need for a portable electronic device that operates effectively for a user in low lighting or complete darkness. In particular, the device should permit the user to activate a button on its keypad merely to turn-on the backlighting system without performing any other operation of the device. For keystrokes entered soon thereafter, the keypad should operate the device as it normally would when there is more ambient lighting. With such a device, the user would not worry about entering characters or activating functions when he or she cannot see the display. There is also a need for a portable electronic device having a backlighting system that illuminates an input device in addition to, or separate from, a display based on ambient lighting conditions in order conserve energy consumption. There is a further need for a portable electronic device having a backlighting system that detect ambient lighting conditions without requiring a light sensor in order to minimize cost and/or the size of the device. The present invention fulfills these needs and provides other benefits as will be apparent from the description herein.